Fix command documentation for publish

[joelverhagen]

Motivation and Context

The --file=PATH pattern does not work. The path is an optional, positional argument not a named option.
The --dry-run option is not supported.

Look at the implementation:

registry/cmd/publisher/commands/publish.go

Line 19 in d092dd6

func PublishCommand(args []string) error {

How Has This Been Tested?

Try these options yourself, they are ignored.

Breaking Changes

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update

Checklist

• I have read the MCP Documentation
• My code follows the repository's style guidelines
• New and existing tests pass locally
• I have added appropriate error handling
• I have added or updated documentation as needed

Additional context

[donnie-msft]

As someone who was relying on this document when working on a release pipeline, I appreciate this update to make it correct!